1. Field of the Invention
The present invention relates to an apparatus for and a method of stabilizing a laser power and frequency from a radio frequency excited laser using an optogalvanic effect, and more particularly to an apparatus and method of laser power and frequency stabilization of a radio frequency excited laser, which only use a variation in incident or reflecting radio frequency signal depending on an optogalvanic effect generated from the laser itself, as a reference for the stabilization, without using signals obtained from partial detection of output laser beam, by a conventional fast infrared detector.
2. Description of the Prior Art
Power and frequency of a laser depends on an interval between two mirrors which constitute a cavity of the laser. Accordingly, the laser power and frequency is stabilized when the above interval, namely, cavity length, is stabilized to be constant. Typically, three stabilization methods have been used to make such a cavity length constant while coping with a variation in the cavity length caused by thermal expansion or vibrations.
The first stabilization method is illustrated in FIG. 9. As shown in FIG. 9, a piezo electric transducer 31 is attached to one of mirrors constituting a laser cavity 100, namely, a mirror 3. When the laser cavity 100 varies in length at a frequency of about 520 Hz, an oscillation of laser output occurs. The output from the laser is split by an optical splitter 12 so that it is partially transmitted to an optical detector 13. The transmitted oscillating signal is detected by the optical detector 13 so that it is subsequently used as a reference signal for a laser power and frequency stabilization.
The second stabilization method is illustrated in FIG. 10. In accordance with this method, a high-voltage direct current (DC) discharge tube 14 is arranged in the laser cavity 100, in place of the optical detector used in the first stabilization method, as shown in FIG. 10. In this case, an oscillating signal generated from the discharge tube 14 is used as a reference signal for a laser power and frequency stabilization.
The third stabilization method is to attenuate all laser outputs with a level higher than a minimum power, using an optical attenuator arranged outside the laser.
The stabilization method, wherein a reference signal for stabilization is generated, based on a signal split from an output from the laser by the optical splitter 12, involves a reduction in laser power because the laser output is partially used. Furthermore, since the optical splitter 12 is arranged on the optical path of the laser, it is difficult to obtain an accurate optical axis alignment for the optical splitter 12. In addition, a variation in the transverse mode of the laser may occur.
The stabilization method, wherein the high-voltage DC discharge tube 14 is additionally arranged in the cavity so as to use an oscillating signal generated from the discharge tube 14 as a reference signal, involves a degradation in the oscillation efficiency of the laser due to the provision of the discharge tube 14.
In addition, the above two methods involve a complex laser arrangement resulting in a frequent failure in laser operation. This results in an increase of costs.
In the case of the method, in which an attenuator is arranged outside the laser to obtain a stabilized laser power, a degradation in laser efficiency occurs because the laser power is optionally attenuated. Similar to the above mentioned methods, the laser arrangement is complex because of the use of the additional unit. As a result, an increase in costs occurs.
In association with the present invention, the following papers have been referenced:
Related Paper
1. A. L. S. Smith and S. Moffatt, "Opto-galvanic stabilized CO.sub.2 laser," Optics comm., Vol. 30, No. 2, pp. 213-218, 1979.
2. Michael J. Kavaya, Robert T. Menzies, and Uri P. Oppenheim, "Optogalvanic stabilization and offset tuning of a carbon dioxide waveguide laser," IEEE J. Quantum Electron., Vol. QE-18, No. 1, pp. 19-21, 1982.
3. T. Suzuki, "Optogalvanic spectroscopy with rf discharge," Optics comm., Vol. 38, No. 5,6, pp. 374-368, 1981.
4. Chin-Chun Tsai, Tyson Lin, Cherng-Yn Shieh, Tsu-Chiang Yen, and Jow-Tsong Shy, "CO.sub.2 laser frequency stabilization using the radio-frequency optogalvanic Lamb dip," Appl. Opt., Vol. 30, No. 27, pp. 3842-3845, 1991.
5. C. Stanciulescu, r. C. Bobulescu, A. Surmeian, D. Popescu, and lovitzu Popescu, C. B. Collins, "Optical impedance spectroscopy," Appl. Phys. Lett. 37(10), pp. 888-890, 1980